Molecular dynamics simulation on creep-ratcheting behavior of columnar nanocrystalline aluminum

Creep-ratcheting deformation behavior of columnar nanocrystalline (NC) Al varying in grain sizes have been studied using molecular dynamics simulations at three different temperatures (300 K, 467 K, and 653 K). The underlying deformation mechanisms of columnar NC Al for two stress ratios of ratcheting are also evaluated in this study. The highest strain accumulation and rapid hysteresis loop proliferation are attained at 653 K. The dislocation density is low at 653 K in contrast to the other two deformation temperatures. The perfect disloca-tions support the creep-deformation process followed by Shockley partial dislocations. It is observed that the cyclic hardening phenomenon at 300 K and the cyclic softening phenomenon at 653 K dominate during creep-ratcheting loading. The specimen fails earlier at higher temperatures owing to the change in the shape of hys-teresis loops. The predominant grain boundary-based deformation mechanisms of columnar NC Al specimens are grain boundary (GB) migration, GB diffusion, GB widening, GB sliding, and GBs merging for all the deformation temperatures. The variation in the extent of deformation with respect to temperatures depends on strain accu-mulation in the plastic region under creep-ratcheting loading.

Automated summary

In this study, the creep-ratcheting deformation behavior of columnar nanocrystalline Al with varying grain sizes was investigated at different temperatures using molecular dynamics simulations. The underlying deformation mechanisms for two stress ratios were evaluated. The results showed that the highest strain accumulation and rapid hysteresis loop proliferation were achieved at 653 K, and the cyclic hardening and cyclic softening phenomena dominated at 300 K and 653 K, respectively. Grain boundary migration, diffusion, widening, sliding, and merging were identified as the predominant deformation mechanisms for all deformation temperatures.